The present invention relates generally to mobile and portable radio systems, and more particularly to circuitry for providing hands-free operation to mobile and portable radio users in such radio systems.
In both radio and land-line telephone systems, a user communicates by means of a handset that includes a speaker at one end which is placed close to the user's ear and a microphone at the other end which is held close to the user's mouth. Thus, the user has only one free hand since the other must be used to hold the telephone handset. In order to provide a greater degree of freedom to the user, speakerphones have been developed for use in land-line telephone systems. A speakerphone is typically coupled to the telephone line and when enabled allows the user to freely move about while still communicating with another party. Such speakerphones typically compare the volume of the two parties and select the party speaking the loudest. These conventional speakerphones work well when utilized with land-line telephones, but may not operate correctly when used with a radio due to the high degree of ambient noise encountered in a vehicle. For example, a high level of ambient noise may cause such speakerphones to always select the hands-free party, totally blocking all communications from the other party.
A form of hands-free operation has been achieved in radio systems by utilizing a foot switch which both activates the radio transmitter and applies the speaker's voice signal thereto. However, whenever the hands-free party wishes to communicate, he must activate the foot switch. Thus, the hands-free party does not have complete freedom of movement as in the case of a speakerphone. Complete freedom of movement is vitally important when the hands-free party is operating a vehicle. The potential distraction caused by the necessity to activate the foot switch can result in an accident and serious personal injury. Thus, neither conventional speakerphones nor foot switch operated transmitters provide the type of hands-free operation that is necessary in a vehicular environment.